In recent years, the rotational speed of a disk and a brushless motor for rotating the disk is increased as the operation of recording and reproducing the disk such as a CD, a DVD or the like becomes faster. At the present time, it is sometimes the case that the brushless motor is rotated at a speed of about 12,000 rpm. As a chucking device that copes with the high speed rotation of the disk, there has been employed a structure that includes a cone having an annular slanting surface for making contact with the entire extension of an inner circumferential surface of a central opening of the disk. The cone is movable along the axis of a shaft serving as a rotating shaft. Furthermore, the cone is axially upwardly biased by a resilient member such as a coil spring or the like (see, e.g., Patent Document 1 for the structure of such a conventional chucking device).
(Patent Document 1) Japanese Patent Application Publication No. 2004-234773
As a disk drive apparatus becomes cheaper, there is an increasing demand for price reduction of the brushless motor with which the disk drive apparatus is equipped.
However, the conventional chucking device with the cone requires the use of an additional clamp member that presses the upper surface of the disk to keep the same in place. In addition, a resilient member such as a coil spring or the like is required in the conventional chucking device, which increases the number of parts of the chucking device. As a result, it becomes difficult to reduce the price of the chucking device, which in turn makes it difficult to achieve price reduction of the brushless motor provided with the chucking device.